Disable the use the proxy port setting for transparent caching
If the use source IP (USIP) option is disabled on a cache service configured on the NetScaler appliance, the appliance forwards client requests to the cache service by using a appliance-owned subnet IP (SNIP) address or mapped IP (MIP) address as the source IP address and a random port as the source port. The randomly selected port is called the proxy port.
However, if you want to configure a fully transparent cache (a cache configuration in which the cache service receives the client’s IP address and port number), you must not only enable the USIP option, either globally or on the cache service, but also disable the Use Proxy Port setting, either globally or on the cache service. Disabling the Use Proxy Port setting enables the appliance to use the client’s source port as the source port when it connects to the cache service, and ensures a fully transparent cache configuration.
For more information about configuring the Use Proxy Port option globally or on a service, see Configuring the Source Port for Server-Side Connections.